1. Field of the Invention
The invention relates to an electrical unit comprising a proximity switch and a cable terminal part and a process for its manufacture. The proximity switch having an outside housing and an insulation part, with the insulation part being on one end face of the outside housing and having a terminal element with terminals which lead to the outside. The terminals of the terminal element which lead to the outside being made as terminal sockets. The cable terminal part having a cable and a connecting part, the cable being mounted in the connecting part and the ends of the leads of the cable being connected electrically to the terminal sockets of the terminal element.
2. Description of the Related Art
The prior art discloses different possibilities for connecting detachable and fixed proximity switches to a cable. Plug-and-socket connections, that is detachable cable joints which are made using plug connectors which can be connected to the terminals of the proximity switch, are known for example in German patents 195 28 678 and 44 19 023 (the latter corresponding to U.S. Pat. No. 5,573,411). Another detachable cable joint, specifically a screw-type terminal, is shown by German patent 195 29 181. A proximity switch with a fixed or non-detachable cable terminal is shown, by way of example, in the German patent 42 25 267 which describes a housing termination comprising hot-melt cement through which the cables, which are connected directly to the electronics in the proximity switch, are routed out of the proximity switch.
Both the detachable joints of cables on proximity switches as well as the nondetachable cable terminals for proximity switches which are known from the prior art have a series of defects.
Detachable joints generally require a relatively large amount of space. Since recently the trend has been toward smaller and smaller proximity switches, only little space is available for one such detachable joint. In designs with plug connectors, it is also disadvantageous that they are much more expensive to manufacture than proximity switches to which the cables are directly connected.
In the last two decades, especially in the field of inductive proximity switches, it has been possible to further increase the operating distance at the same outside diameter of the coil which is used for the inductive proximity switch. This means that at a uniform operating distance the outside diameter of the proximity switch which is essentially dictated by the coil diameter has been reduced. This is advantageous to the user, but entails problems in forming connections, particularly with smaller devices, which are conventionally made in thread sizes M 6 to M 12. That is for cable terminal or plug terminal technology, the maximum plug diameter in cylindrical proximity switches generally will not be greater than the threaded or smooth sleeve diameter of the proximity switch in order to enable any installation in walls of different thickness.
In proximity switches with a non-detachable cable terminal, either the cable is permanently connected to the electronics and then the entire electrical unit after adjustment is inserted into the housing of the proximity switch and potted, or the electronics in the housing of the proximity switch is connected via flexible wires to the cable or plug, and only after final testing are the cables and plugs mechanically connected non-detachably and permanently to the housing, for example, by potting. These types of direct connection enable the shortest overall lengths, due to the long wires however a large amount of space is necessary.
Since the users of proximity switches, when selecting one type of proximity switch, ask for very many cable colors, cable materials and cable sizes which are different from one another, the diversity of types of proximity switches provided with a nondetachable cable is quite large; this leads to considerable warehousing costs for storage of all the conceivable types of proximity switches.